The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. As of 2021, the British Army comprises 82,040 regular full-time personnel, 3,960 Gurkhas, and 29,740 reserve personnel.
The modern British Army traces back to 1707, with antecedents in the English Army and Scots Army that were created during the Restoration in 1660. The term British Army was adopted in 1707 after the Acts of Union between England and Scotland. Members of the British Army swear allegiance to the monarch as their commander-in-chief, but the Bill of Rights of 1689 and Claim of Right Act 1689 require parliamentary consent for the Crown to maintain a peacetime standing army. Therefore, Parliament approves the army by passing an Armed Forces Act at least once every five years. The army is administered by the Ministry of Defence and commanded by the Chief of the General Staff.
The British Army, composed primarily of cavalry and infantry, was originally one of two Regular Forces within the British military (those parts of the British Armed Forces tasked with land warfare, as opposed to the naval forces), with the other having been the Ordnance Military Corps (made up of the Royal Artillery, Royal Engineers, and the Royal Sappers and Miners) of the Board of Ordnance, which along with the originally civilian Commissariat Department, stores and supply departments, as well as barracks and other departments were absorbed into the British Army when the Board of Ordnance was abolished in 1855 (various other civilian departments of the board were absorbed into the War Office).
The British Army has seen action in major wars between the world's great powers, including the Seven Years' War, the American Revolutionary War, the Napoleonic Wars, the Crimean War and the First and Second World Wars. Britain's victories in most of these decisive wars allowed it to influence world events and establish itself as one of the world's leading military and economic powers. Since the end of the Cold War, the British Army has been deployed to a number of conflict zones, often as part of an expeditionary force, a coalition force or part of a United Nations peacekeeping operation.
The British Army is made up of the Regular Army and the Army Reserve. The army has a single command structure based at Andover and known as "Army Headquarters". Deployable combat formations consist of two divisions (1st Armoured and 3rd Mechanised) and eight brigades. Within the United Kingdom, operational and non-deployable units are administered by two divisions, Force Troops Command, and London District.
The Army has 50 battalions (36 regular and 14 reserve) of regular and reserve infantry, organised into 17 regiments. The majority of infantry regiments contains multiple regular and reserve battalions. Modern infantry have diverse capabilities and this is reflected in the varied roles assigned to them. There are four operational roles that infantry battalions can fulfil: air assault, armoured infantry, mechanised infantry, and light role infantry. Regiments and battalions e.g.: the Parachute Regiment, exist within every corps of the Army, functioning as administrative or tactical formations.
Armoured regiments are equivalent to an infantry battalion. There are 14 armoured regiments within the army, ten regular and four yeomanry (armoured reserve), of which four are designated as "Armoured", three as "Armoured cavalry", and six as "Light Cavalry". Army 2020 Refine has seen developments which will further modify the Royal Armoured Corps. with two existing regiments forming the core of two new STRIKE Brigades. These two regiments, along with the Armoured Cavalry will be equipped with the "Ajax" armoured fighting vehicle, a new £3.5 billion procurement programme. The Ajax will be employed in the task organisation and roles of both Armoured Cavalry and Medium Armour. With a slight exception of the Household Cavalry, which maintains quasi-autonomy within the Household Division, armoured regiments and their yeomanry counterparts collectively form the Royal Armoured Corps.
Arms and support units are also formed into similar collectives organised around specific purposes, such as the Corps of Royal Engineers, Army Air Corps and Royal Army Medical Corps.